The present invention relates to a sealing film for toner cartridge ensuring the formation of an opening with a substantially constant width after tearing a central longitudinal portion of said sealing film.
Up to now many researches have been made in order to find a sealing film for sealing a toner cartridge, which is flexible and which after longitudinal tearing, is suitable for defining an opening with a substantially constant width.
Prestel at al (U.S. Pat. No. 5,110,646) discloses a sealing member not having a preferred tearing direction, which is provided with a series of adjacent perforations Such perforations cause leakage of toner particles, whereby the use of such sealing member has not be considered as useful by the man skilled in the art.
Films having a preferred tearing linear direction are nowadays used extensively for sealing toner container. However, even with means for lowering the initial tearing force, the opening formed after tearing a central strip is reduced most of the time, some times increased, from the initial tearing end up to the terminal tearing end.
For ensuring a substantially constant width of the opening formed after tearing a central strip from the sealing film, EP-0 788 033 (Canon) has proposed to use a sealing film comprising a base layer having a tearing directionality, a guide layer having a tearing guide portion formed by a laser processing, and a laser barrier layer provided between said base layer and said guide layer. Such a film is expensive and the risk to have an undesired tearing is high as the base layer and barrier layer can induce an undesired tearing.
Tests made by Applicant have shown that when a film with a tearing directionality is provided with two grooves parallel to the preferred tearing direction, a constant width of the opening formed after tearing the central strip could not be ensured.
It has now been observed that when making cuts or grooves perpendicular to the preferred tearing direction of the film and when tearing the strip in a direction perpendicular to the preferred tearing direction, it was possible to obtain an opening with a substantially constant width.
It has also been observed by Applicant that by selecting the correct material for the sealing member, it was possible to avoid the problem of contamination of the toner with fibrous material.
The invention relates to a sealing film for toner cartridge, said film having a longitudinal portion to be torn out, said longitudinal portion extending between a first line and a second line and to be torn between a first end and a second end, wherein said sealing film comprises a layer with a thickness comprised between 20 xcexcm and 1 mm and with a preferred substantially linear tearing direction. Said layer is provided at least with a first longitudinal surface recess, such as a groove, preferably a cut, extending along the first line and a second longitudinal surface recess such as a groove, preferably a cut, extending along the second line, whereby said longitudinal surface elements extend in a direction of at least 5xc2x0 with respect to the preferred substantially linear tearing directions.
The total thickness of the sealing film or at least of the portion thereof to be torn out is preferably lower to 400 xcexcm, such as lower than 300 xcexcm, lower than 200 xcexcm. Examples of thickness are 30 xcexcm, 50 xcexcm, 75 xcexcm, 100 xcexcm, 120 xcexcm, 150 xcexcm, 175 xcexcm.
The film can have a laminated structure, but has preferably a structure comprising at most two laminated layer. When the film is a laminated structure of two layers having parallel tearing directions, it is advantageous to provide the film on both faces with surface elements selected from the group consisting of cuts, grooves, recesses and combinations thereof.
A preferred substantially linear tearing direction is the direction along which a linear tear line extends due to a tearing force.
The layer provided with the longitudinal surface elements (cuts, grooves, recesses, combinations thereof) is preferably a layer which requires means for lowering the initial tearing force, such as cuts, perforations, etc.
Advantageously, said longitudinal surface cuts, grooves, recesses or combinations thereof form an angle comprised between 5xc2x0 and 175xc2x0 with respect to the preferred substantially linear tearing direction and extend partially into the thickness of the layer so as not to transverse the layer.
Advantageously, the longitudinal surface cuts, grooves, recesses or combinations thereof form an angle between 45xc2x0 and 135xc2x0 with respect to the preferred substantially linear direction.
Preferably, the longitudinal surface cuts, grooves, recesses or combinations thereof form an angle of about 90xc2x0 with respect to the preferred substantially linear direction.
Advantageously, the longitudinal surface cuts, grooves, recesses or combinations thereof extend at least at a distance of more than 1 cm from the first end of the portion.
Preferably, the longitudinal surface cuts, grooves, recesses or combinations thereof are associated with a means for lowering the initial tearing force.
For example, the cuts, grooves, recesses or combinations thereof are located on a face of the film intended to be directed towards the toner cartridge.
According to a specific embodiment, the first and second longitudinal surface cuts, recesses or grooves are substantially perpendicular to the preferred linear tearing direction, while said first and second longitudinal surface cuts, grooves or recesses extend substantially from the first end up to the second end.
According to a possible embodiment, the film comprises a first series of longitudinal surface cuts, grooves or recesses extending along the first line and a second longitudinal surface cuts, grooves or recesses extending along the second line.
For example, the cuts, grooves or recesses of a series are spaced from each other with a distance of less than 10 mm, advantageously of less than 2 mm, preferably of less than 1 mm.
According to a detail of a embodiment, the cuts, grooves or recesses have a maximum depth corresponding to 75% of the thickness of the layer.
According to another detail of an embodiment, at least one portion of cuts, grooves or recesses has a minimal depth corresponding to at least 10% of the thickness of the layer, preferably corresponding to at least 20% of the thickness of the layer, most preferably corresponding to at least 30% of the thickness of the layer.
The cuts, grooves or recesses may have a constant or variable depth.
The film is preferably a monolayer film provided with adhesive means. The film can be a bi-directional film. The adhesive can be a contact glue, a pressure glue, a hot-melt glue, etc. The adhesive, preferably the hot-melt adhesive can be associated to heating means (which can be removed or not from the adhesive after a heating step), such as conductive means, conductive layer, electric conducting wire or layer, etc. Such adhesive (with or without heating means or removable heating means) can also be used in sealing member comprising a multilayered film.
The monolayer film has advantageously a thickness of less than 400 xcexcm, preferably of less than 300 xcexcm, such as 25 xcexcm, 40 xcexcm, 50 xcexcm, 70 xcexcm, 90 xcexcm, 110 xcexcm, 125 xcexcm.
The sealing film is advantageously provided with adhesive means and with a removable protecting layer to be removed for attaching the film on the toner cartridge.
The sealing film is preferably provided with a pulling means connected to the portion to be torn. The pulling means is for example a portion of the film, or can be a band attached to the strip to be torn.
The layer is for example a layer selected from the group consisting of uniaxially oriented polyethylene film, uniaxially oriented polypropylene film, bi phase polymer film, films made of incompatible compounds, biaxially oriented polypropylene, biaxially oriented polyethylene, and mixtures thereof. The layer can be reinforced (for example with a mat of fibres, a non woven material or fabric), non reinforced, laminated or not laminated, glued or not glued to a flexible support, etc.
The invention relates also to a toner container or a toner cartridge comprising a sealing film of the invention, as disclosed here before.
The invention further relates to a method for opening a sealing member of a toner cartridge or container, in which the central strip is torn out in a direction different from the preferred tearing direction of the film.
It has also been observed that the tearing is facilitated or more precise, when reinforcing the lateral edges of the pulling means of the sealing strip, when the pulling means is integral with the sealing member. The invention relates thus also to a sealing member provided with an integral pulling means, the lateral edges of which are reinforced.